The cancer-fighting power of antioxidants has been thrown into doubt by US research that shows they can also help cancer cells to survive and thrive.

But, Australian experts say the findings should not alarm cancer patients as the research is laboratory based and the results may not replicate in people.

Antioxidants, which are common in fruit and vegetables, include beta-carotene, and vitamins A, C and E.

According to the US National Cancer Institute, antioxidants protect against cancer by stabilising molecules, known as free radicals, which can cause damage to cells.

In a study published online today in the journal Nature, Harvard Medical School Professor Joan Brugge says antioxidants can help cancer cells to stay alive and sometimes encourage tumour development.

Tumour independence

Normal epithelial cells die off if they become detached from a supporting structure known as the extracellular matrix.

Tumour cells overcome this by developing 'anchorage independence', which allows them to survive outside the matrix.

It has previously been known that in breast cancer, cancer-causing genes such as erbB2 help detached tumour-generating cells to survive.

But Brugge's team found that antioxidants also help promote this characteristic in tumour-causing cells.

They also found the antioxidants allow new tumours to develop by helping cells that are metabolically damaged during detachment.

Brugge says the antioxidants seem to do this by boosting the energy levels of the damaged cells through the oxidation of fatty acids.

Dr Mark Waltham, head of the Pharmacogenomics Laboratory at St Vincent's Institute in Melbourne, says the study further "muddies the water" on the benefits of antioxidants for people with advanced cancer.

"Despite a lot of belief that antioxidants are cancer suppressing, this is raising the possibility that consuming antioxidants may make cancers more malignant," he says.

Waltham says one of the main causes of death from cancer is metastasis where the cancer spreads to secondary sites.

"In order for a tumour to get to a secondary site it has to survive as a sole entity," says Waltham.

"This study raises the possibility that antioxidants are permitting tumour cells to have increased survivability when they detach from the primary site."

Beyond the lab

Although Brugge says the findings are important in better understanding cancer biology, she says there are no immediate implications for cancer patients.